Apparatus for gas analysis



Nov. 27, 1945. P. s. WILLIAMS ETAL 2,339,706.-

APPARATUS FOR GAS ANALYS IS Filed Jan. '7, 1943 II- V mm mmummazom hm Eoumu 2 553: mm, :5 SEE. 2 mm 5 mm mu Nu muzzommzh. m. mum? u r EEK .vN dS Patented Nov. 27, 1945 APPARATUS FOR GAS ANALYSIS Philip S. Williamsand Monroe W. Kriegel, Tulsa, Okla., assignors to Standard OilDevelopment Company, a corporationot Delaware Application January 7,1943, Serial No. 471,528

Claims.

The present invention is directed to a readily portable apparatussuitable for analyzing combustible gases. More specifically, theapparatus is particularly suitable for analyzing the amount ofhydrocarbons present in soil air.

Apparatus designed for the analysis of soil gas samples is now wellknown to the art. However, these known arrangements are quite bulky andare usually placed in a centrally located laboratory, requiring thecollection of samples in the field andthen transportation of the samplessubstantial distances to the laboratory. The apparatus of the presentinvention is a compact unit which may be readily transported so that thesamples may be analyzed in the field.

Other objects and advantages of the Present invention may be seen from areading of the following description taken in conjunction with thedrawing, in which the sole figure diagrammatically illustrates apreferred embodiment of the present invention.

Referring specifically to the drawing, numeral II is a connectionsuitable for attaching pipette 9 containing the sample of soil air tothe apparatus. A suitable means of attaching the sample-containingvessel to the apparatus is by rubber tubing l9. Flow of fluid throughline II is controlled by suitable cocks, l2 and 3, and a manometer I4connecting into the line at a point between the two stopcocks. Line l9connects with scrubber i5 which in turn is in communication withscrubber It. The purpose of scrubber i5 is to remove carbon dioxide fromthe sample while scrubber I 6 removes water vapor therefrom. It ispreferred to employ askerite for the removal of the CO2, and phosphoruspentoxide for the removal of water vapor.

A means for evacuating the apparatus is provided, including a mercurydifiusion pump 28 and a mechanicall operated fore pump 29 adapted toback up the mercury diffusion pump.

Between the evacuation means and scrubber it are arranged two branches.One branch comprises only a conduit controlled by stopcock i8. The otherbranch includes triple trap 19, and a U tube 25 and is arranged forfluid communication with Pirani tube assembly 22, oxygen containingreceiver 24 controlled by stopcock 23 and manometer 3|. Flow of fluidthrough this second branch may be controlled by stopcock i1- and by amercury valve which will be hereafter described.

The mercury valve includes U tube 25 and a mercury containing reservoir32 immediately below the U tube and in communication therewith by meansof a vertical length of tubing. The upper portion of reservoir 32 abovethe mercury is provided with an outlet to the atmosphere controlled bystopcock 26. This space above the mercury in the reservoir may also beconnected with pump 29 through a two way stopcock 21.

By means of the connections above described,

a single mechanical pump may be employed both,

to operate the mercury valve and to back up the mercury diffusion pump.Any time the pressure in line 25 is below atmospheric the mercury valvemay be closed to prevent communication between triple trap I9 anddifiusion pump 28 by setting two-way stopcock 21 to preventcommunication between reservoir 32 and pump 29 and thereafter openingvalve 26. The atmospheric pressure will force mercury from the reservoirupwardly into the U shaped trap 25. When it is desired to open themercury valve, stopcock 23 may be closed and stopcock 21 set to allowcommunication between pump 29 and the upper portion of reservoir 32.This allows pump 29 to reduce the pressure above the mercury reservoirand mercury will flow from U tube 25 into the reservoir to allowcommunication between triple trap l and diffusion pump 28. a

It will be understood that the mercury valve may be operated in arelatively short space of time and that during the interval in whichreservoir 32 is in communication with pump, 29 the mercury diffusionpump 28 may continue to operate without being connected to pump 29. Whenthe space above reservoir 32 has been evacuated the stopcock 21 maybe-turned to again allow communication between diffusion pump 28 andmechanical pump 29. In this manner, pump 29 serves both to back upmercury diffusion pump 28 and operate the mercury valve without allowingair from the atmosphere to get into-the diffusion pump.

The Pirani tube assembly 22 consists of a pair of Pirani tubes with oneconnected to the vacuum system as illustrated, and. the otherpermanently reduced to a very low pressure. The Pirani tube assembly isprovided with usual electrical equipment, including filament wireswhereby the change in heat conductivity between the filament .wires andthe bulbs to the atmosphere is measured to indicate the pressure in thesystem.

Triple trap I9 is provided with electrodes 20 and 2|. These electrodesare electrically connected to a suitable means for supplying a highvoltage current, for example, high voltage transformer 30. When thetriple trap has been evacuated to a very low pressure, a high voltagemay be impressed across the electrodes tocause combustion of the sample.It is preferable to use a potential of the order of 15,000 voltsfor-causing this combustion. a

In conducting an analysis with the apparatus described, a pipette 9 ofknown volume is employed. This allows the weight of soil air in thesample to bedetermined by calculation. The pipette is then attached tothe apparatu in the manner shown in the drawing, and triple trap I! thenchilled by immersing it in liquid nitrogen. Stopcocks i8 and I3 are thenclosed and stopcock i2 opened to allow the sample to expand. Withevacuating pump 29 in operation, stopcock I3 is then opened slowly andthe sample allowed to pass through the ascarite and phosphorus pentoxideinto the trap I8, the completeness of the removal 01 the sample from thepipette being noted by observing the reading of manometer it. As thesample passes through trap l9, all hydrocarbons heavier than methane arecondensed therein.

When the pressure throughout the system has been reduced toapproximately 25 millimeters of mercury, valve I1 is closed and thepressure on the trap I9 is further reduced to substantially zero. TrapI9 is then isolated from the evacuating pump by closing the mercuryvalve, and oxygen is then allowed to enter the trap from reservoir 24 bymanipulating valve 23, until the pressure within the trap is about sixmillimeters as shown by manometer 3|. The hydrocarbon gases within trapiii are then burned by discharging a high voltage through the trap byconnecting transformer 30 to a suitable source of electrical power notshown. It has usually been found that an initial discharge voltage of15,000 is suflicient to pass a discharge through the trap, l9.

It is preferred to remove the liquid nitrogen bath from trap I9 at thesame time the electrical discharge between electrodes 20 and 2| isinitiated. This allow the trap to be warmed to room temperature whilethe burning is proceeding. At the same time the discharge is takingplace cock I8 is opened to allow the evacuation of reagent traps l andi6.

After the combustion within trap I9 is complete, the circuit is brokenand the trap immersed in a bath of liquid nitrogen to condense carbondioxide and water vapor formed by combustion of the sample. It has beenfound in usual operations that a discharge of high voltage through thetrap for a period of one minute produces satisfactory combustion of thesample. After the carbon dioxide and water vapor have been condensed inthe trap l9, excess oxygen is pumped oil by means of the evacuationsystem through U tube 25. The mercury valve is then closed, and theliquid nitrogen bath adjacent trap I9 is replaced by a bath of dry iceand acetone, which allows the trap to be warmed to -80 C. With the trapmaintained at this temperature by the mixture of dry ice and acetone,the pressure of 00: therein is measured by means of the Pirani tubeassembly 22. Since the volume of the system in communication with thePirani tube system has been previously determined, the amount of CO2present may be determined from a reading of the pressure by means of thePirani tube assembly. 'The results are preferably expressed on the basisof total combustible carbon in the sample in parts per million parts ofinitial sample by weight.

Having fully described and illustrated the practice of the presentinvention, what we desire to claim is:

1. An assembly adapted for analyzing gases comprising in combination ascrubbing means, an evacuating means including a mercury difluslon pumpand a mechanical pump, a first conduit and a second conduit eachconnecting said scrubbing Y means with 'said diflusion pump, a stopcockcontrolling fiow in each of said conduits adjacent said scrubbing means,a triple trap and U tube inserted in the first conduit, a reservoir, aconduit connecting the reservoir with the first conduit, a pressuregauge assembly, a conduit fluidly connecting the assembly to the firstconduit between said triple trap and said U tube, a mercury reservoirarranged adjacent said U tube, a conduit fluidly connecting a lowerportion of the U tube with a lower portion of the reservoir, a conduitarranged for connecting said reservoir with said mechanical pump, astopcock in said conduit, a conduit having a stopcock therein connectingan upper portion of the reservoir with the atmosphere wh'ereby mercurymay be forced into and removed from said U tube.

2. A device in accordance with claim 1 in which said triple trap isprovided with spaced electrodes therein and a source of high voltageelectrical power is electrically connected to said electrodes.

3. An assembly adapted for analyzing gases comprising in combination, ascrubbing means, a mercury diffusion pump, a mechanical pump, a firstconduit connecting the scrubbing means with the diiiusion pump, astopcock in the first conduit, a second conduit connecting the scrubbingmeans with the diffusion pump, a U tube in the second conduit, a trap inthe second conduit between the U tube and the scrubbing means, astopcock in the second conduit between the trap and the scrubbing means,a mercury reservoir, a third conduit connecting a lower portion of the Utube with a lower portion of the reservoir, a fourth conduit connectingan upper part of the reservoir with the atmosphere, a stopcock in thefourth conduit, a branched conduit defining passages between thediflusion pump and the mechanical pump, and between an upper portion ofthe mercury reservoir and the mechanical pump, and a stopcock in thebranched conduit arranged to connect selectively either the reservoir orthe difiusion pump with the mechanical P p.

4. A device in accordance with claim 3 in which the trap is providedwith spaced electrodes therein and a source of high voltage electricalpower is electrically connected to said electrodes.

5. In an assembly adapted for analyzing gases and including a vessel anda mercury difiusion pump, means defining paths of fluid flow between thevessel and the diffusion pump including a first conduit and a secondconduit fluidly connected to form a loop, a stopcock in the firstconduit, 9. U tube in the second conduit, a stopcock in the secondconduit between the U tube and the vessel, a mercury reservoir adjacentthe U tube, a third conduit fluidly connecting a lower portion of thereesrvoir with a lower portion of the U tube, a fourth conduit fluidlyconnecting an upper portion of the reservoir with the atmosphere, astopcock in the fourth conduit, a, mechanical pump, a branched conduitdefining a path of fiuid communicating between the diffusion pump andthe mechanical pump and between an upper portion of the reservoir andthe mechanical pump and a valve in the branched conduit arranged toconnect selectively either the reservoir with the me-- chanical pump orthe diifusion pump with the mechanical pump.

PHILIP S. WILLIAMS. I MONROE W. KRIEGEL.

